Poly-alpha-olefin composition stabilized with beta,beta&#39;-thio-dibutyrates



United States Patent U.S. Cl. 26045.85 6 Claims ABSTRACT OF THE DISCLOSURE A poly-a-olefin composition containing as a stabilizer .001 to 3% by weight based upon the polyolefin of a dialkyl-[3,B-thio-dibutyrate wherein the alkyl groups contain from to 30 carbon atoms.

This invention relates to a poly-a-olefin composition which is resistant to degradation due to light, heat and oxygen.

More particularly, it relates to a poly-a-Olefin composition which is resistant to degradation due to light, heat and oxygen and which does not cause sweating-out (exudation) of a stabilizer constituent on the surface of shaped articles made thereof by incorporating therein a di-higher alkyl-B,fi-thio-dibutyrate as an essential stabilizer ingredient.

Polyolefins such as polypropylene, polyethylene, co polymer of ethylene and propylene or the like cannot withstand the ordinary hot processing operation without sustaining serious impairments of their physical properties when they are to be made into mold articles, fibers, films or the like. Even after fabrication, articles manufactured from poly-a-olefins are subject to changes in their physical appearance and properties, due to their exposure to sunlight, heat, oxygen and the like. This change or degardation in the properties of the polyolefin material has, in the past, impaired its use as a basic manufacturing material. In order to improve the properties of poly-a-olefins it has been a common practice to add various light stabilizers and antioxidants to the poly-aolefin compositions. For example, additives such as dialkyl-figfi'-thio-dipropionate including the dilauryl and distearyl derivatives in combination with various phenolic derivatives such as 4,4-butylene-bis(6-t-butyl-m-cresol) and 2,6-di-t-butyl-p-cresol have been used as stabilizers for poly-a-olefins. In addition to the foregoing, many other compounds and combinations of compounds have been added to poly-a-olefins to stabilize them and increase their resistance to ultra-violet light degradation. A constant drawback to the use of the various prior art stabilizers has been the problem of the sweating out of the stabilizers on the surfaces of the shaped articles, and the concurrent loss of their stabilizing properties. It is therefore apparent that the invention of a stabilizer that will not exude from the poly-a-olefin in which it is incorporated would represent a significant advance in the art.

An object of this invention is to provide a poly-u-olefin composition resistant to deterioration due to light, heat and oxygen and a method for producing the same by incorporating therein a novel and inexpensive stabilizer alone or together with another stabilizer which stabilizer will not sweat out of the shaped POlY-oc-Olfi1l. It has now been found such an object can be attained by the present invention.

According to present invention, poly-a-olefin copolymers can be stabilized much more effectively than with any other prior art stabilizers, by incorporating therein a novel compound, a di-higher'alkyl-13,5-thio-dibutyrate. The di-higher alkyl-5,5'-thio-dibutyrate may be used alone to stabilize poly-a-olefins or may be used in combination with other heretofore recognized stabilizers.

'Ihese di-higher alky1-fl,;8'-thio-dibutyrates have a general formula:

wherein R is an alkyl group having from 10 to 30 carbon atoms, preferably from 12 to 20 carbon atoms. When the number of carbon atoms in the alkyl group, R, is less than 1-0 the esters are undesirably volatile, have an unpleasant odor during heat processing, and tend to exude on the surface of the fabricated articles. As the number of the esters exude on the surfaces of the polyolefin articles. As the carbon atoms increase to more than 30, the esters become unsuitable, because of the difliculty of their manufacture. When the number of carbon atoms constituting R is less than 10 the ester is a liquid at room temperature while when R is more than 14 the esters are solids. For example, dii'sodecyl-B, 3'-thio-dibutyrate is liquid at room temperature and the melting points of dilauryl-, dicetyl-, and distearyl-5,B-thio-dibutyrate are 2628 C., 394l C., and 54-56 C., respectively.

Representative examples of the di-higher alkyl-thiodibutyrates of the invention include; di-normaland di-iso-alkyl esters of fl,B'-thio-dibutyric acid, such as didecyl, diisodecyl, dilauryl, diisolauryl, dimyristyl, -diiso- I pentadecyl, di-2,2-dimethyl dodecyl), dicetyl, distearyl,

dieicosyl, dihexacosyl esters. Suitable esters are selected from among them according to the kinds of poly-u-olefins, conditions of treatments, conditions of their uses or the like.

Di-higher alkyl-13,3-thio-dipropionates which are conventionally used, require a relatively expensive acrylic acid as a starting material, the total yield is low in their manufacture, and the stabilizing effect is insufficient, whereas di-higher alkyl-3,3'-thio-dibutyrates of the invention require an inexpensive crotonic acid as a starting material, the total yield is high in their manufacture and the stabilizing effect is far superior to those of the thiodipropionate esters.

The additional methyl groups in the chemical structure of the thio dibutyrates of this invention are probably somewhat responsible for the superior stabilizing effects of these compounds over the conventional thio dipropionates.

Di-higher alkyl-5,B-thio-dubutyrates can be produced by various methods which can be summarized as follows: These esters can be produced (1) by e'sterifying B,5-thioldibutyric acid with a saturated aliphatic alcohol containing 10-30 carbon atoms, or (2) by making di-lower alkyl- 3,5'4hio-dibutyrate carrying out an ester-exchange reaction with a saturated aliphatic alcohol, or (3) by reacting crotonic acid or lower alkyl crotonate with a saturated aliphatic alcohol and then reacting the resultant higher alkyl crotonate with H 8 in the presence of a catalyst.

As between the above processes, the reaction of higher alkyl crotonates with H 8 in the presence of a catalytic amount of alkali metal alcoholate is preferable because of its superior production yield.

The di-higher alkyl-fi,;3'-thio-dibutyrates of the present invention are incorporated in poly-a-olefin copolymers, alone or together with an effective phenolic stabilizer, in

an amount of 0.001%-3% by weight based upon the polymers. Examples of the effective phenols include:

2.6-di-t-butyl p cresol, 2.4-dimethyl-6-t-butylphenol, 2.4-dipropyl--methylphenol, 3-methyl-4-isopropylphenol, 2.6-di-t-butyl-2-methoxy-p-cresol, 2.2'-methylene bis[4- methyl-6-t-butylphenol], 2.2 methylene-bis [4-ethyl-6-t- 5 food packaging. By the use of a higher alkyl ester of 5,5- butylphenol], 4.4-methylene-bis[6-t-butyl-o-cresol], 4.4'- thio-dibutyric acid, the above-mentioned drawback of methylene-bis[2.6-di-t-butylphenol], 2.6-bis[2 hydroxyexudation can be completely overcome. 3-t-butyl-5-methyl-benzyl] -4-methyl phenol or the like. The following examples are given in order to illustrate Besides the above-mentioned phenols, auxiliary agents 10 the present invention but it is to be understood that they such as calcium stearate, aluminum stearate or the like, are not intended as limitations thereof. and further, necessary, additives such as inhibitor, EXAMPLE 1 corrosion inhibitor, antistatic agent, plasticizer, slipping agent, filler or the like can be incorporated therein. To 100 Parts of crystalline P yp py (intrinsic The stabilizer can be incorporated in the polyolefin by Y 7 Were added following Stabihlers dissolving the stabilizer in a suitable solvent such as ben- Solved in heIlZeIle- The mixtures were kneaded to the PaSte zene and mixing the resultant solution with the polyolefin form and dried and further ed in vacuo at ro m temfollowed by the evaporation of the solvent, or by merely perahlffi- Then ey ar Pressed at for five millmixing the stabilizer alone with a polyolefin with stirring, and further P ssed at a pressure of 200 kg./cm. or by adding the stabilizer to the polyolefin at the end of for five minutes to give sheets having thickness f 1 mmolymerization stage.

p As poly-a-olefins which can be stabilized by the present Test Items stabilizer, polypropylene, polyethylene, and ethylene-pro- (1) Thermal resistance (Oven life). samples were 93,161.13 copolymer are preferable and Polypropylene are put on an aluminum dish placed in an oven through which particularly preferred However poly'a'olefins such as air heated at 154 C. is recycled. The times elapsed until poly'4'methyl'pentene poly cracks were formed on the surface were measured. pentene'l poly 'f poly octenefl' (2) Weather resistance.A weatherometer (B.P.T. 75 Poly'decene'l or the or copolymer (contam C., carbon arc) was used. The times elapsed until samples mg graft block copolymer) also can be used were broken by 90 bendings were measured.

As above-mentioned, the di-higher alkyl-13,B'-thiodibutyrates of the invention are far superior in their stabilizing effect than the other polyolefin stabilizers which are generally used, such as diesters of 18,;3-thio-dipropionic which is frequently encountered with the use of conventional stabilizers. For example, when stearyl ester of 3,13- thio-dipropionic' acid is used as a stabilizer for polypropylene film, the stabilizer is exuded on the surface of film. This is a fatal drawback in the use of plastic films for (3) Coloring.-The effects on the coloring of the sheets were observed over a 96-hour thermal resistance test period and a 200 hour weather resistance test period. Experimental results were as follow:

TABLE 1 Thermal Weather Coloring states I resistance resistance in the said 96 Experiment No. Blending recipe (part per 160 parts of polypropylene) period (hr.) period On.) and 200 hours 1 DLTDP, 0- 290-305 360-370 2 DSTDP, 0-5 150-160 275-290 3.- DMTDB, O 5 405-410 760-770 4 DCTDB, 0 375-385 840-850 5 DS'IDB, 0.5 385-390 685-690 N h 6.- DLTDP, 0.25 plus (BHT, 0.1; Q-158, 0. mm aarsso ange- 7 DSTP, 0.25 plus (BHT, 0.1; Q-158, 0.2; Cast, 0. 630-650 360-370 8 DMTDB, 0.25 plus (BHT, 0.1; Q 158, 0.2; 0381;, 0.15) 1, 020-1, 030 515-530 DOTB, 0.25 plus (BHT, 0.1; Q-l58, 0.2; CaSt, 0.15) 965- 640-650 10 DSTB, 0.25 plus (BHT, 0.1; Q-l58, 0.2; 09.51;, 0.15) 1, 010-1, 020 525-530 NOTE:

DLTDB-Dilauryl-B,B-thio-dipropionate.

DSTDP-Distearyl-B,B-thio-dipropionate.

DMTDB-Dimyristy1B,fl-thio-dibutyrate (the invention ester).

DCTDB-Dicetyl-5,B-thiodibutyrate (the invention ester).

DSTDBDistearyl-B,fl-thio-dibutyrate (the invention ester).

BHT-2.6-di-t-butyl-p-cresol.

Q-158-A phenolic compound containing zinc and phosphor.

Cast-Calcium steai'ate.

acid. Comparative tests in which dilauryl-fi,p'-thio-dipro- 55 EXAMPLE 2 pionate and dicetyl-;8,}8'-thio-dibutyrate, alone or combined with 2.6-di-t-butyl-p-cresol have been incorporated in a crystalline polypropylene are as follows:

To 100 parts of ethylene-propylene copolymer containing 5% of ethylene and 95% of propylene were added No'rE.-The heat degradation tests: Samples were placed in a test tube and heated at 54 C. Times elapsed until cracks are formed by 90 bendings were measured. The light degradation tests: Samples were irradiated by iadometer (carbon arc) and heated at 63:1: 5

0. Times elapsed until cracks are formed by 90 bendings were measured.

The important advantage gained by the use of higher the stabilizers shown in the following table. Test pieces alkyl ester of B,fi'-thio-dibutyric acid as a stabilizer of were made from the resultant mixture by the same manner polyolefin is that the stabilizer will not elude, a problem as in Example 1.

Experimental results TABLE 2 Thermal Weather Coloring state Blending recipe (part) (ethyleneresistance resistance in the said 96 Experiment No. propylene eopolymer 100 parts) period (br.) period (hr.) and 200 hours 1 DLTDP, 0.5 255-260 415-420 2 DLTDB, 355-360 580-590 3.. DMTDB 0 5-- 345-355 770-775 4 DCTDB, 0.5-- 335-350 820-830 5-- DSIDB, 0.5 375-385 690-700 No Chan 9 6-- DLTDP, 0.5 plus Ethyl A-702, 0.25.- 640-650 390-400 g 7-. DLTDB, 0.5 plus Ethyl A-702, 0.25- 960-080 630-640 8-- DMTDB, 0.5 plus Ethyl A-702, 0.25.--" 980-1, 000 680685 9-. DCTDB, 0.5 plus Ethyl A-702, 0.25. 960-980 660-670 10 DSTDB, 0.5 plus Ethyl A-702, 0.25 980-1, 010 760-765 N MEL-Ethyl A-702-4,4-methylene-bis-(2.6-di-t-butylphenol).

EXAMPLE 3 To 100 parts of crystalline polypropylene were added the following stabilizers, and test pieces were made and tested in the same manner as in Example 1.

Experimental results gradation due to light, heat and oxygen containing a nonexuding stabilizer comprised of a di-higher alkyl-}3,fithio-dibutyrate of the general formula,

TABLE 3 Thermal Weather Experiment Blending recipe (part per 100 parts of resistance r i ta P yp py period (br.) period (br.)

1 DLTDP, 0.5 plus BHT, 0.25 450-4 0 210.220 2 DLTDB, 0.5 plus Santowhite, 0.25 1, 110-1, 120 530.540 3 DCTDB, 0.5 plus Santonox R, 0.2 1,140-1,155 550 555 4 DCTDB, 0.5 plus Topanol CA, 0.25. 1, 12o-1,130 365.375 5 DCTDB, 0.5 plus Irganox 565, 0.25 740-745 320330 6 DCTDB, 0.5 plus Irganox 858, 0.25.. 1, 020-1, 030 320.330 7 DSTDB, 0.5 plus Irganox 1076, 0.25. 1, 450-1, 4 5 3504,55 8 DSTDB, 0.5 plus Irganox 1093, 0.25. 900-910 400.410 9.- DSTDB, 0.5 plus Antioxidant 80, 0.25. 600-610 350-3 0 10. DSTDB, 0.5 plus Antigen W, 0.25. 730-745 350-37 1 DSTDB, 0.5 plus Nonfiex, 0.25. 720-730 350-350 1 DSTDB, 0.5 plus Antioxidant 423, 0.25- 990-1, 000 350-350 N on:

Santowhit e-4,4-butylidene-bis(3-methyl-6-t-butylphenol) Santonox R-4,4-thio-bis(3methyl-Frt-butylphenol).

Topanol CAl,1,3-Tris(2-methyl-5'1:-butyl-4-hydroxy-phenyDbutane. Irganox 565-2,4 bis (n-octylthio)-6-(4-hydroxy-3,5-di-t-butyl-anilino)-1,3,5-triazine. Irganox 858-4-n-octylthio-2,6-bis(4-hydroxy3.5-di-t-butyl-anilino)-1,3,5-triazine.

Irganox 1076-4-hydroxy-3,5-t-butylphenyl-propionic acid-stearyl. Irganox 1093-4-hydroxy-3,5-t-butylbenzyl-dialkylphosphite.

Anitoxidant S0-2,6-bis(2-hydroxy-3-t-butyl-5-methylbenzyl)-4-methy1phenol.

Antigen W4,4'-eyc1ohexyl-bisphenol. Nonflex-Stylenized phenol. Antioxidant 423-A phenolic compound.

TABLE 4 Thermal 1 Blending recipe (part per 100 parts of resistance Experiment No. polypropylene) period (br.)

1 DL'IDP, 0.025 210-220 2-- DSIDP, 0.025. 240-250 3 DLTDB 0.025 330-340 4 DCTDB, 0.025 350-360 5-- DSTDB, 0 02' 330-340 6- DLTDP 0 025 plus BHT 0 025 380-300 7. DSTDP, 0 025 plus BHT 0 0 380-390 8 DLTDB, 0.025 plus BHT 0.025- 550-560 9. DCTDB, 0.025 plus BHT 0.025 550-560 10 DSTDB, 0.025 plus BHT 0.025 530-540 1 Thermal resistance tests were carried out at 125 C.

What is claimed is: 1. A poly a-mono-olefin composition resistant to deatoms, in an amount of 0.001 to 3% by weight based upon said polyolefins.

2. A composition according to claim 1 wherein said stabilizer comprises dilauryl-B,;8'-thio-dibutyrate.

3. A composition according to claim 1 wherein said stabilizer comprises dimyristyl-fi,j3'-thio-dibutyrate.

4. A composition according to claim 1 wherein said stabilizer comprises dicetyl-fi,l3'-thio-dibutyrate.

5. A composition according to claim 1 wherein said stabilizer comprises distearyl-,3,fl'-thio-dibutyrate.

6. A composition according to claim 1 in which said poly-wmono-olefin is crystalline polypropylene.

References Cited UNITED STATES PATENTS 3,196,185 7/1965 Ranson 260-619 3,255,136 6/1966 Hecker et al. 260-23 3,227,676 1/1966 Mills et a1. 260--45.85

HOSEA E. TAYLOR, IR., Primary Examiner US. Cl. X.R. 260-4535, 23, 396 

